Electric retardation line



G. W. PIERCE ELECTRIC RETARDATION LINE "March 9, 1926. I 1,576,459

Filed Dec. 24, 1921 l ments,sa1d mutual Patented Mar. 9, 1926.

UNITED STATES 1,576,459- PATENT OFFICE.

GEORGE W. PIERCE, OF CAMBRIDGE, MASSACHUSETTS,'ASSIGNOR TO SUBMARINESIG- NAL COMPANY, OF PORTLAND, MAINE, A CORPORATION OF MAINE.

ELECTRIC RETARDATION LINE.

Application filed December 24, 1921. Serial No. 524,807.

To all whom it may concern:

Be it known that I, GEORGE W. PIERCE,

a citizen of the United States, residing at Cambridge, Middlesex County,Massaclur,

setts, have invented a new and useful Im provement in ElectricRetardation Lines, of which the following is a full, clear, and exactdescription. I I

The present invention relates to electric retardation lines, and moreparticularly to a retardation linefor introducing definite timeretardation of electric currents in a manner such that currents of acomplex character will be retarded in a rational and predeterminableway, without essential distortion, over a significantrange offrequencies. tion results in a considerable extension over previousretardation lines the range of frequencies for which the -1 etardation"time is independent of frequency. I

The present invention is an improvement over the artificial retardationline disclosed in my pending application, Serial No. 306,- 689 filedJune 25, 1919, for electric compensators. The present invention,however, is not limited to the application of the retardation lineherein disclosed, to an electric compensator, as the present inventionis capable of wider application and may be employed wherever anartificial line isdesired which will retard electric currents withoutessential distortion over a considerable range of frequencies.

In my application for electric compensators I showed an artificial line'consisting of inductance elements .in" series and capacity elements inshunt for introducing predetermined elements of time retardation intoelectric currents transmitted through the artificial line. v

The present invention relates particularly to the introduction into sucha line of mu-' tual induction-between the inductance eleinductancebeingproperly roportioned to the self-inductance of t e elements. I havediscovered that the mutual inductance between inductive elements, orcoils, of such a line, if given a certain unique relation to theself-induc- The present invendispersionless herein as descriptive of aline or system through which a complicated wave form may pass and beessentially preserved in its wave form in that the different significantfrequency components of the wave form pass with essentially equal timeretardations. The significant frequency components are those which arenecessary or desirable in the electric current for the purposesemployed. For example, in electric current of audible frequency used inconnection with auditory translalting devices, such as telephonereceivers, the signiti cant frequency components of the wave form arethe audible or principal audible frequency components.

In the drawings, Figure 1 is a diagram showing an artificial lineillustrating the present invention; and Figure 2 is a detail view insection indicating diagrammatically a mounting of the inductance coils.

Referring to the diagrammatic illustration of the invention, anartificial line is illustion of the line which contains the retarda-Theretardation line is made tion sections. up of a plurality ofrecurrent sections each comprising an inductance 3 in series with theline and a capacity 4 shunted across the line. In the diagrammaticillustration five sections are illustrated, it being understood,however, this is merely for the purpose of illustration and that inpractice the number of sections will generally considerably exceed this,depending of course upon the purposes for which ihe line is used and theamount of time retardation desired. I When the retard-.tion line is tobe used in an electriccompensator as shown, for example, in my electriccompensator application Serial No. 306,689 referred to -above, the linewill vbe provided with the necessary taps and contacts whereby thenumber of effective sections may be varied at will. The inductance coils3 are preferably placed end to end, and may be wound on a common core,as indicated schematically in Figure 2. The showing in Figure 2isintended merely as a general diagrammatic illustration and it will beunderstood that in winding and mounting the coils, the diameter of thecoils, the size of Wire, the spacing of the coils apart, etc., will becalculated in accordance with the formulae hereinafter referred to. Thewindings of adjacent coils are so spaced from one another that themutual inductance between adjacent coils 3 is approximately one-tenth ofthe self-inductance of each coil. The-computation of this 1 to 10relation is based on the following considerations.

Let L be the self-inductance of each of the inductance coils. M be themutual inductance between adjacent coils, and, as notation, let

where wzthe angular'velocity of asinusoidal electromotive force.impressed at the input end of the line, and, as furthernotation, let

Logw

then, we have In equations (4:) and (5) a is the attenuation constantand w the retardation angle introduced by the line into the current persection of the line. The same sign must be employed before the innerradical in the two equations, and that sign must be selected to If nowwe temporarily let take the sine of both sides of (5), square both makea and 5 both real quantities; The sides, and expand the result in seriesfor equations (4) and (5) are exact. values of A greater 1 we obtain Letus now expand Q, as defined by equation (3), in the form and write (7 inthe form where F LC w and G M02602- (1 1) Now substituting (10) into(9), and keepmg only significant terms, we obtain make the retardationangle (p proportional to a); and since F is proportional to m equa-;

tion (12) suggests the advisability of makmg It is seen that (14) leadsto a these conditions (16) gives, in view of (11) M:L/12, approximately.If now we replace L by its value from (1), we obtain M:L,/10,approximately. (17) Therefore, if we make the line to have betweenneighboring coils a mutual inductance, as given by (17),approximatelyequal to one-tenth of the self-inductance of each coil, we shall havethe effect that the range of frequencies over which the time retardationper section is essentially independent of the frequency is much greaterthan the .range with M equal to zero as in the practice heretofore. Infact the specific value of M given by equation (17) is uniquely the bestvalue to give to M to make the line one of low dispersion.

Equation (17 is stated only approximately, in that this value may beshifted slightly one way or the other tomake slight adjustments-for someof the small neglected terms- Also in practice, it may be desirable forstructural reasons to depart somewhat from (17).

To obtain the time retardation T per section of the line, it is onlynecessary to divide the retardation angle (p by the angular velocity to.By (13) and (11) this operation gives forv a significant range offrequencies T: L, +2lVl)O J w/5; provided M 1/ The principles of theabove mathematical discussion are to be found in my book entitledElectric Oscillations and Electric Waves published by McGraw-Hill BookCo. Inc. New York, 1920, and particularly in Chaper XVI and specificallyon page 316 and following. On page 316 of this book,

sion, the words and if there is no magnetic leakage should be strickenout, as I have found that the results are general. Reference may be madeto this book for details of the principles above treated.

Itwill be noted that the present invention constitutes a transmissionline of low dispersion, and in addition to this important feature it hasthe advantage of being easier and cheaper to construct than a linewithout the novel feature of properly propor-' tioned mutual inductance,in that the coils maybe wound in solenoidal form and may be compactlyarranged which obviates the expense of toroidal windings or of widespacing as must be employed in artificial lines not having my novelfeatures.

It willbe seen by computation or experiment that a slight departure, forexam-' ple 10 percent, from the relation M=L,/l0 may be made with onlyslight departure from the low dispersive effect of the line.

For general computations as to attenuation, retardation, and surgeimpedance of the lineand apparatus of the present invention use may bemade of sections 283, 28 1 and 285 of my book abovereferred to, whichsections are contained on pages 316 and following. In using thesesections for calculation of apparatus of the present invention, thevalue M L /lO, or in case of a small departure from this relation thevalue of M specifying the departure, should be employed and substitutedinto the formulas of the book.

By having the induction coils with the mutual inductance relation asspecified in this application, the range of frequencies for which thedispersion is low and practically insignificant may be from three to tentimes as great as the range for lines without the mutual inductance. As'above pointed out the present invention, however, is not limited to theuse of a, retardation line in an electric compensator. shown in myelectric compensator application, but the apparatus and method of thepresent invention is one of general application. It is to be understoodthat the present inven ion is not so limited but relates to aretardation line, or artificial electric line, and its method of usebroadly as set forth in the following claims:

I claim:

1. An electric retardation line having capacities in shunt andinductance elements in series and having the mutual inductance betweenadjacent inductance elements approximately equal to one-tenth of theself-inductance of the elements, substantially as described.

2. An electric retardation line having 'capacities in shunt andinductance elements in series, having the self-inductance betweenneighboring points of attachment of the ca.-

pacities approximately ten times the mutual inductance between theinductance elements, substantially as described.

3. An electric retardation line having low distortion and comprisingcapacities in shunt and inductance coils in series having their self andmutual inductances so proportioned that the line is substantially dispelsionless as well as of low distortion over a considerable range ofsignificant frequencies, substantially as described.

4. An electric retardation line comprising a series of recurrentsections each comprising a capacity shunted across the line and aninductance coil in series with the line and so located with relation toadjacent sections as to have mutual inductance therewith in theneighborhood ofone-tenth of its self-inductance, substantially asdescribed.

5. An electric retardation line comprising a series of recurrentsections, each having a capacity shunted across the line and an'inductance in series with the line permitting the substantially freepassage of alternating located with respect to each other as to l havesuch mutual inductance as to minimize dispersion of the significantfrequency components of the current waves, substantially as described.

6. An electric retardation line having capacities in shunt andinductance coils in series, the inductance coils each havingsubstantially the same self-inductance and each pair of adjacent coilshaving substantially the same mutual inductance, the self andmutualinductance being so proportioned that the line is substantiallydispersionless over a considerable range of frequencies, substantiallyas described.

7. An electric retardation line comprising a series of recurrentsections, each comprising a capacity shunted across the line and aninductance in series with the line so located as to have mutualinductance with the inductance coils of adjacent sections in substantialaccordance with equation est-pea. aigret. t -(1...)!

so that the retardation angle is approximately proportional to theangular velocity over the significant range of frequencies,substantially as described.

8. An electric retardation line comprising a series of recurrentsections, each including a capacity shunted across the line and aninductance in series with the line and whose retardation angle persection is an antisine function of the frequency of the impressedclectrolnotive force, the inductances of adjacent sections being solocated with respect to each other as to reduce said retardation angleto substantial proportionality to said frequency, substantially asdescribed.

In testimony whereof I have hereunto set my hand.

GEORGE W. PIERCE.

